What is the best variant of darknet to use?
I used Trieu's Darkflow and it was trained well up to around 30 to 50 epoch with maximum 30 GB dataset. At the same time, it was quite often crashed after these epochs. 

Half precision...I don't remember Darkflow have that. 

One way to estimate each fork reputation is by number of Star and Issues, for example Alexey's Darknet 5,000 and 2,500 and Darkflow 5,000, 539 respectively. 

Reference: OS Ubuntu 16.04